// Copyright (c) 2006-2024, Timothy A. Davis, All Rights Reserved.
// SPDX-License-Identifier: LGPL-2.1+
// https://github.com/DrTimothyAldenDavis/SuiteSparse/tree/dev/CSparse/Source
import { csTdfs } from './csTdfs.js';

/**
 * Post order a tree of forest
 *
 * @param {Array}   parent          The tree or forest
 * @param {Number}  n               Number of columns
 */
export function csPost(parent, n) {
  // check inputs
  if (!parent) {
    return null;
  }
  // vars
  var k = 0;
  var j;
  // allocate result
  var post = []; // (n)
  // workspace, head: first n entries, next: next n entries, stack: last n entries
  var w = []; // (3 * n)
  var head = 0;
  var next = n;
  var stack = 2 * n;
  // initialize workspace
  for (j = 0; j < n; j++) {
    // empty linked lists
    w[head + j] = -1;
  }
  // traverse nodes in reverse order
  for (j = n - 1; j >= 0; j--) {
    // check j is a root
    if (parent[j] === -1) {
      continue;
    }
    // add j to list of its parent
    w[next + j] = w[head + parent[j]];
    w[head + parent[j]] = j;
  }
  // loop nodes
  for (j = 0; j < n; j++) {
    // skip j if it is not a root
    if (parent[j] !== -1) {
      continue;
    }
    // depth-first search
    k = csTdfs(j, k, w, head, next, post, stack);
  }
  return post;
}